A standard process for making glass fibers is to pull molten glass from a melting furnace through devices referred to as bushings. Bushing devices include plates, located at the discharge area of the furnace, which contain a plurality of closely spaced, relatively small orifices or tips through which the molten glass is pulled. The glass is pulled in continuous filaments or fibers, and the plural filaments are gathered and wound onto a spool for later use. Between the bushing orifices, or tips, and the winding apparatus, the glass filaments are attenuated, followed by coating with a sizing material.
Greater industry demand for glass fibers has resulted in the development of glass melters having bushings with an increased number of orifices or tips, thus creating a greater filament discharge per furnace (throughput). However, larger bushings have led to uneven heat patterns across the bushing; thus, the pulled glass filaments typically are of different temperatures as they exit the bushing. Moreover, the filaments are pulled at a greater throughput than in the past, thus requiring more efficient heat quenching thereof. The glass fibers must be properly cooled to achieve proper attenuation, and the cooling must be achieved taking into account the increased bushing size and increased throughput, as well as uneven temperatures in the glass filaments.
Prior cooling systems have utilized jets for blowing gas on the glass fibers as they exit the bushing. See, for example, U.S. Pat. No. 3,988,135. The use of a gas stream directed at the emerging filaments can cause the filaments to bend or to otherwise move. Clearly this is disadvantageous to maintaining uniform glass filaments.
The use of finshields having heat-absorbing fins attached to a fluid-cooled manifold and located adjacent to the area from which the filaments exit the bushing represents an attempt to cool the fibers so as to achieve proper attenuation. See U.S. Pat. No. 3,264,076. This method uses fins which are pre-angled along the finshield so as to accommodate the filaments being pulled at an angle as they are gathered below the tip plate. This method has served to lower the filament temperatures for proper attenuation only in furnaces having relatively lower outputs, fewer bushing tips, and moderate throughput speeds. Attempts to use these conventional finshields in processes with large bushings and high throughput speeds have encountered numerous problems.
For example, because they are being gathered from larger tip plates, steeper angled blades are required for the outermost filaments. However, increasing the angle of the blades increases the risk that, after a process interruption, the emerging beads may contact the fins, agglomerate, stick to the blades, and result in a flooded tip section.
Accordingly, the increased demand for glass fibers and resultant increase of bushing sizes and throughput speeds has created a need for improved heat-absorbing finshield devices in cases where dimensional constraints limit the use of thicker or larger fins to provide increased cooling capacities.